Is it possible to change sim card on unlocked gsm pre 2

I've been using an unlocked GSM palm pre2 here in the UK for the past few months and am loving it. When I first activated it I used an orange payasyougo sim card, but the cost of internet access is turning out to be really high for my needs. I've just found a good deal through a different carrier (three) with as much as you want data/month and am wanting to switch. How do I change my phone number and will I lose all my paid apps. I'd read that the webos profile is linked to the imei number of the phone and not to the sim but on the hpwebos account page it only allows you to edit passwords and email addresses. Although there is an ominious looking button with which I can delete my account. I don't want to press that button if it means I lose all my apps. Any help/info/advise would be greatly appreciated.